Direct injection engines are engines wherein fuel injection occurs inside the engine's cylinders. Injection of the fuel in this manner allows for more precise control over fuel consumption. Direct injection reduces cylinder temperature and improves air-fuel mixing allowing for greater power, improved emissions, and improved fuel economy. However, engines of this type are also very prone to inlet (also called intake) valve deposits (IVD). These deposits can interfere with valve closing, valve motion, and valve sealing, which reduces the efficiency of the engine and limits maximum power.
U.S. Patent application 2004/0198614, Calder et al., Oct. 7, 2004, discloses a method of reducing intake valve deposits (or inlet valve deposits, IVD) by utilizing a lubricating composition wherein the base oil contains combinations of Group III and/or Group IV base oils in combination with Group V synthetic ester base fluids.
U.S. Patent application 2006/0052252, Wedlock et al., Mar. 9, 2006, discloses a method for lubricating a gasoline direct injection (GDI) engine with a lubricant containing a combination of low viscosity base oil derived from a Fischer-Tropsch process and a high viscosity oil also derived from a Fischer-Tropsch process.
U.S. Patent application 2005/215441, Mackney et al., Sep. 29, 2005, discloses a method of operating a direct injection engine having an exhaust gas recirculation system by introducing via the fuel an ashless detergent that results in improved performance of the lubricant.
U.S. Patent application 2006/0172896, Conroy et al., Aug. 3, 2006, discloses a method of reducing the occurrence of ring-sticking in an internal combustion engine by using a lubricant containing a relatively large amount (1-15% wt) of a low molecular weight (Mn 100 to 5000) olefin polymer, especially polyisobutylene.
U.S. Pat. No. 6,034,039, Gomes et al., Mar. 7, 2000, discloses complex overbased detergents made up of combinations of sulfonate and phenate soap that provide enhanced corrosion and deposit control.
WO/PCT application 2005/061682, Wilby et al., Aug. 23, 2006, discloses lubricant formulations containing detergent compositions and dispersants designed for improving cleanliness and deposit control. Detergents derived from alkyphenols provide especially good cleanliness.
Olefin copolymers are well known as viscosity modifiers in lubricant compositions. They can be used to improve viscosity index, provide thickening of the composition, or allow for the formulation of multi-grade lubricants. Various characteristics of these materials, including molecular weight, may be controlled at levels suitable for use at treat levels necessary to impact the viscosity of the lubricating composition in the desired way.
Conventional ethylene-olefin copolymers at typical treat levels (0.1% to 2% by weight) do not solve the problem of inlet valve deposits (IVD) in direct injection engines. The present invention provides a lubricating composition with a relatively small amount (from 0.005 up to 1.0 or 0.5 or even 0.1% by weight) of high molecular weight polyolefin that reduces IVD.
Historically, metal-containing detergents have been used to improve deposit control. However, in GDI engines, increased levels of detergent metal (or ash) results in higher levels of inlet valve deposits. Metal-containing detergents are necessary in a lubricant to provide basicity (known as TBN) to control corrosion, wear, and other degradation pathways. It has been discovered that the use of high molecular weight polyolefins, especially polyisobutylene, in combination with metal-containing detergents in the lubricant composition results in reduced oil misting and reduced IVD and allows for the use of higher levels of ash-containing detergents.